1. Field of the Invention
The present invention relates to an inkjet print apparatus, and particularly to an inkjet print head and an inkjet print apparatus which are provided with a plurality of print elements for scanning a print medium to spatter liquid droplets thereon.
2. Description of the Related Art
In recent years, in an inkjet print apparatus for performing a print by ejecting liquid droplets, the small-sized of the ejection liquid droplet is in progress. This is because, since a landing-on dot size formed at the time ejection liquid droplets land on a liquid droplet receiving member can be made small owing to the small-sized of the liquid droplet, a high-definition image can be formed to make an expression of a contour or an expression of a color tone enriched. However, even if the ejection liquid droplet is made small to improve a print concentration, it is important not to reduce the output time. Conventionally in a so-called multi-pass print of performing a plurality of times of scans on the same print location to complete a print, an image is formed by more print-pass numbers for producing a high-quality image, but an attempt of reducing the print-pass number has been recently made for realizing a print in high speeds.
In this way, the inkjet print technology is under the circumstance where targets of high image quality and high speeding are oriented to be simultaneously achieved. For realizing this high-speed print, for example, measures of performing a reciprocal print, increasing a carriage speed and the like are taken. However, in a case of increasing the carriage speed, since a region for the drawing per unit time is widened, it is necessary to increase the number of liquid droplets ejected from a nozzle per unit time, that is, it is necessary to make the ejection frequency be high.
On the other hand, this inkjet print has a phenomenon that extremely minute liquid droplets generated followed by ink ejection from nozzles float without reaching a liquid droplet receiving member. In regard to this phenomenon, due to a tendency of the increase in the ejection frequency in addition to the small-sized of the liquid droplet described above, an increase in the number of the aforementioned floating minute liquid droplets (hereinafter, called also floating mists) generated per unit time is remarkable. In addition, there are some cases where the minute liquid droplets are more likely to be generated depending on ink properties to be used so that the phenomenon that the liquid droplets become the floating mists remarkably occurs. The existence of these floating mists is one of problems in the product design.
An example of a problem caused by this floating mist is shown in the following. In an inkjet print system, print heads are mounted on a carriage to scan a print medium and at the same time, ink droplets are successively ejected from an ejection opening provided in the print head to perform a print on the print medium.
FIG. 17A and FIG. 17B are diagrams each schematically showing a state where a conventional print head 7 ejects ink while moving in a direction shown by an arrow α. Under a print condition where a drive frequency per nozzle is high, such as in a case of a solid print, a flow 502 curling up in an ejection opening forming face (hereinafter, called also head face) direction of the print head 7 is, as shown in FIG. 17A, generated between the print head 7 and a print medium 1 in the middle of printing. It should be noted that in the following drawings, in a case of simultaneously expressing the print head 7 and the flowing place, the flowing state is expressed by a coordinate system fixed in the print head 7 for convenience.
The aforementioned floating mists 504 rise by the flow 502 to be attached on the head face. Then, in the vicinity of the ejection nozzle line, a wet portion 11 of the ink is formed by the attached floating mists 504 to raise a problem of deterioration in image quality due to a mixed color and an ejection defect. The problem of this ink wetting is a big barrier to realizing a small number of the passes with the high image quality being maintained. Since the attachment of the floating mist 504 on the head face is a phenomenon generated in the middle of printing, the event that the attachment of the floating mists 504 cannot be avoided even by suction and wiping performed at the time the print head 7 is returned to a home position is a big problem.
For overcoming these problems, for example, Japanese Patent Laid-open No. 2004-025718 discloses a mechanism of collecting floating mists inside the print apparatus by sucking and discharging air inside the print apparatus by a suction fan arranged at an end portion of the print apparatus. However, the effect of reducing the attachment of the floating mists on the head face can not be expected. Japanese Patent Laid-open No. 2004-306270 proposes a method in which suction openings are provided between the respective print heads, and the floating mists are sucked by a fan connected to this suction opening.
In the construction of Japanese Patent Laid-open No. 2004-306270, since it is necessary to install the fan, it leads to generation of noises, an increase in size of the apparatus and an increase in costs. Further, since suction of air is forcibly performed in the vicinity of the ejection opening, there is a possibility that not only a track of the floating mists but also a track of ink droplets forming an image by landing on a print medium are shifted. In the construction of Japanese Patent Laid-open No. 2004-042580, an air resistance reducing unit is provided in a carriage bottom or in a print head side portion to restrict turbulence of the air, thus performing a reduction in a generation amount of mists to be generated in the print head. However, even if the generation amount of the mists is restricted, the attachment of the floating mists having been generated is not restricted.
The reduction in an amount of floating mists to be attached on the head face is thus still a difficult technology and a problem to be solved.
FIG. 18 is diagram showing the conventional print heads and shows the construction where a plurality of print heads are provided. There are some cases where the problem of the head face attachment of the floating mists clearly occurs in an inkjet print apparatus constructed of the print heads as shown in FIG. 18. It should be noted that in the following specification, an x axis is defined as a scan direction of the print head, a z axis is defined as a direction vertical to the print medium, and a y axis is defined as a direction at right angles to an x-y plane.
In a case of n pieces of print heads as shown in FIG. 18, a flow 406 curling up followed by ink ejection of a first print head 181 is weak and an attachment amount of mists on a head face is small. On the other hand, since flows 407 and 408 curling up are stronger in a second print head 182 to an nth print head 183 after the first print head 181 than in the first print head 181, more floating mists are resultantly attached on the head face. There is a tendency that a phenomenon that this attachment amount increases becomes furthermore marked in each print head in the order from forward to backward print heads in the scan direction. Therefore, the event itself that the floating mists are attached on the head face is a problem, but in a case where the plural print heads are provided, the event that the attachment amount of the floating mists on the head face differs in each print head also causes a difficulty in designing.
As described above, in the inkjet print apparatus with the plural print-head construction, there occurs the problem that the floating mists are more likely to be attached on the head face in each of the print heads subsequent to the print head positioned in the head in the scan direction to cause deterioration in print quality thereof.